In a communications system, when faults occur at transport network nodes or links, protection switching needs to be performed, that is, a service on the path with the fault is handed over to a pre-assigned standby path for transportation, thereby not affecting transmission of the service.
The protection switching has different protection types, which mainly include 1+1 protection, 1:n protection, and m:n protection. In the protection switching of the 1:n protection type, n work transmission entities share one protection transmission entity, that is, at the same moment, only one normal service can be protected, in which n≧1. Under a normal situation, the normal service is transmitted on the work transmission entity, and an extra service or no service is transmitted on the protection transmission entity. When the fault is detected on one work transmission entity, the normal service originally transmitted on the work transmission entity is switched to the protection transmission entity on an ingress node and an egress node of a protection domain. Here, if an extra service is originally transmitted on the protection transmission entity, the extra service is cut off.
The service switching is implemented through cooperation work of the work transmission entity, the protection transmission entity, a bridge on the ingress node, and a selector on the egress node. Two types of bridges, namely, a selective bridge and a broadcasting bridge, may be adopted on the ingress node.
Referring to FIG. 1, a schematic view of a 1:n protection switching system using a broadcasting bridge on an ingress node is shown.
When a work transmission entity normally works, the ingress node only sends a normal service on the work transmission entity through the bridge, and an egress node receives the normal service from the work transmission entity through a selector. Here, a protection transmission entity may or may not transmit an extra service. When the extra service is transmitted, the ingress node transmits the extra service on the protection transmission entity through the bridge, and the egress node receives the extra service on the protection transmission entity through the selector.
When a fault occurs at the work transmission entity, the egress node determines that a Signal Fail (SF) or Signal Degrade (SD) fault occurs at the work transmission entity through fault detection or performance monitoring on the work transmission entity. If the fault does not occur at the protection transmission entity at this time, the ingress node transmits the normal service on the work transmission entity and the protection transmission entity simultaneously through the bridge. If the extra service is originally transmitted on the protection transmission entity, the ingress node further needs to cut off the transmission of the extra service. The egress node receives the normal service on the protection transmission entity through the selector, thereby completing protection switching.
Referring to FIG. 2, a schematic view of a 1:n protection switching system using a selective bridge on an ingress node is shown.
When a work transmission entity normally works, the ingress node only sends a normal service on the work transmission entity through the bridge, and an egress node receives the normal service on the work transmission entity through a selector. Here, the protection transmission entity may or may not transmit the extra service. When the extra service is transmitted, the ingress node transmits the extra service on the protection transmission entity through the bridge, and the egress node receives the extra services on the protection transmission entity through the selector.
When an SF or SD fault occurs at the work transmission entity, if the fault does not occur at the protection transmission entity at this time, the ingress node switches the normal service originally transmitted on the work transmission entity at which the fault occurs to the protection transmission entity through the bridge for being transmitted. If the extra service is originally transmitted on the protection transmission entity, the ingress node further needs to cut off the transmission of the extra service. The egress node receives the normal service on the protection transmission entity, thereby completing protection switching.
For the SD fault, the prior art may have the following disadvantages.
In a packet-based network, fault detection of a transmission entity is performed according to whether an egress node receives a connectivity detection packet in a preset time, so as to determine whether an SF fault occurs at the transmission entity; and performance monitoring, for example, monitoring on a packet loss ratio, of the transmission entity is performed according to a service packet, so as to determine whether an SD fault occurs at the transmission entity. The transmission entity always sends the connectivity detection packet for performing the fault detection. When an ingress node uses a broadcasting bridge and a protection transmission entity does not transmit any extra service, under a normal situation, if performance degrade occurs at both a work transmission entity and the protection transmission entity, the work transmission entity is in the state of SD fault. Because the extra service is not transmitted on the protection transmission entity, the performance monitoring cannot be performed on the protection transmission entity, even if the performance degrade occurs at the protection transmission entity, the state of the protection transmission entity is still normal instead of showing the SD fault. If the protection switching is triggered when the SF fault is not shown at both the protection transmission entity and work transmission entity, it is possible that the normal service protection is switched to the protection transmission entity with the poorer performance when the performance degrade occurring at the protection transmission entity is more serious than the performance degrade occurring at the work transmission entity, as shown in FIG. 3, that is, an invalid service switch is performed, thereby further lowering the service quality.
When the ingress node uses a selective bridge, in addition to the disadvantages of the broadcasting bridge, if the SF or SD fault occurs at the work transmission entity, and the protection switching is performed, the ingress node only transmits the normal service on the protection transmission entity through the bridge. Because the service is not transmitted on the work transmission entity, the performance monitoring cannot be performed. Even if the performance degrade exists on the work transmission entity, the state of the work transmission entity is normal instead of showing the SD fault. Therefore, for a recoverable protection switching, the normal service may be switched back to the work transmission entity from the protection transmission entity. After the normal service is switched back to the work transmission entity, the performance degrade may be monitored on the work transmission entity, the state of the work transmission entity is the SD fault, the protection switching is performed again to switch the normal service to the protection transmission entity, as shown in FIG. 4. Thus, frequent switching of the normal service between the work transmission entity and the protection transmission entity is resulted, thereby seriously lowering the service quality and increasing system burdens.